A number of companies, such as IBM and Packard-Hughes, produce high density flexible electrical cables, often referred to as "flex cable", for use in routing electronic data. These cables have the capability of routing data at high rates of up to Gigabits per second. The cable is relatively flat and resembles a thick stiff belt in appearance and it may be bent around corners or wrapped, much like an ordinary leather belt. The flex cables pack a large number of separate insulated electrical lines within the flex cable's limited width, typically at a line density greater than eighty signal lines per inch. In its construction, the flex cables employ a polyimide film, a strong flexible plastic insulating material, as the dielectric substrate and outer insulating wrap. The electrical lines are lithographically defined and are formed of a very thin and narrow metal strips upon the dielectric substrate and a covering layer of the same material is laminated to that substrate covering the metal strips.
The foregoing flex cables may be designed to have low thermal conductivity, a characteristic which makes the cable ideal for cryogenic applications. The cables can be used to connect cryogenic electronics apparatus, superconducting electronic apparatus, cryo-CMOS circuits and cooled GaAs amplifiers, which a cryogenic refrigeration system maintains at very low cryogenic temperatures during operation, to other external electronic components and circuits that are maintained at room temperature. Since the cable doesn't conduct significant external heat to the cryogenic apparatus, the cable does not create an undue heat load on the cryogenic refrigeration system.
For expeditious cable connection and/or disconnection, electrical connectors are employed with the cable. Respective lengths of cable are wired into respective electrical connectors and the lengths of cable are interconnected by connecting the two mating electrical connectors together, as is conventional practice in the electronic field.
As is elementary, an electrical connector contains a sufficient number of spaced electrical contacts, enabling each connector contact to be electrically connected to a respective electrical lead in the cable. A cable to cable connection is made by mating two connectors or connector portions, as variously termed, together, to form the connector system or connection, and bridging the multiple electrical paths from one cable to another through the connector contacts. To avoid possible confusion in this description, it is appropriate to remind the reader that each mating half or portion of a connector is customarily also referred to as a connector. When reference is made to connector, thus, the reader should be certain to understand the context in which the reference is made to understand whether reference is being made to a connector portion or to the connector system.
The electrical connectors used by the afore-recited flex cable manufacturers to connect flex cables together or to connect flex cables to rigid printed circuit boards employ a "pressed contact" arrangement. The pressed contact arrangement is not the typical male-female prong and socket contact arrangement found in conventional electrical connectors, in which a prong contact frictionally engages within a socket contact. Instead, in the situation in which two flex cables are to be joined, two substantially identical relatively planar thick rigid printed circuit boards, containing the requisite number of electrical lines formed slightly protruding above the circuit board's planar surface serve as the mating connectors. And, in the situation in which a flex cable is to be connected to a printed circuit board, the flex cable and the rigid printed circuit board, containing the requisite number of electrical lines protruding slightly above the planar surface of the circuit board, serve as the mating connectors.
As those skilled in the art appreciate, for a cable to cable connection, the electrical lines plated upon each of those circuit boards is aligned and soldered or otherwise joined to corresponding electrical leads at an end of an associated flex cable, typically by conventional soldering techniques. One of the circuit boards in the connector is inverted relative to the other and, with the electrical lines on the circuit boards aligned, the boards are pressed into engagement to place the respective lines in electrical contact and form the electrical connection. To complete the connector, a mechanical fastening system, including alignment pins and a pressure pad of elastomeric material clamps the mated connector portions together and maintains the respective parallel conductors in contact under a positive pressure or force. The surface of pressure pad contains a series of minute elastic rubber-like bumps or fingers to press against the top of one of the circuit boards, providing, thus, the pressed contact arrangement.
Although the foregoing connector design serves well at room temperature, at cryogenic temperature the connector, and, particularly, the connector's elastomeric pad, often fails to function properly. At cryogenic temperature, the elastomeric material forming the pressure pads becomes brittle and loses its ability to maintain adequate pressure on the circuit boards. As example, where the connector connects eighty or so electrical lines in a high density flex cable, should any one of those electrical lines fail to connect through the connector to an associated line, the connector is deemed to have failed. The loss of any electrical path through the connector cannot be tolerated. Thus, although available flex cable is ideal for application in cryogenic devices, presently available connectors for those flex cables are unsuited for use at those very low temperatures.
When the foregoing connector fails, it must be replaced. To do so requires the cable to be disconnected from the old structure and reattached and soldered to the replacement or requires a new cable to be attached and soldered. In addition to requiring new connectors, that procedure also requires considerable time and expense.
An object of the present invention, therefore, is to provide a new connector system for flex cable that functions at cryogenic temperatures.
A further object of the invention is to provide a connector system that may be easily repaired or reconstructed, without requiring cable rewiring anew, should the connector system fail.
Another object of the invention is to provide a connector system that adapts flex cables to cryogenic device application and may be used in cryogenic systems.
And a still further object of the invention is to provide a positive pressure contact type connector that does not incorporate elastomeric material or any other material that becomes brittle or disfunctional at cryogenic temperatures.